Contrasting ISNULL() versus COALESCE() Performance

Andy Brownsword takes a peek:

When eliminating NULL values with SQL Server queries we typically reach for ISNULL or COALESCE to do the job. Generally speaking they’ll provide equivalent results, but they work in different ways. If you’re dealing with logic more complex than ISNULL(ColA, ColB) – for example using a function or subquery as part of the expression – then you might be in for a surprise.

The content of expressions when evaluating NULL values can have big implications on query performance. In this post we’ll look at how the functions work and the implications they can have when evaluating NULL values.

Read on for the performance showdown.